Memory for cache locations in Merriam's kangaroo rats

Abstract

The ability of Merriam's kangaroo rats, Dipodomys merriami, to remember the location of food caches and to relocate caches in the absence of the odour of buried seeds was examined. Eight wild-caught kangaroo rats cached seeds in an experimental arena, and retrieved them 24 h, later. Before retrieval, all odours associated with the cache sites were removed and seeds were replaced in only half of the cache sites. During retrieval, kangaroo rats were significantly more likely to search cache sites, with or without seeds, than non-cache sites. Non-cache sites were primarily investigated after all cache sites had been searched, indicating that search of non-cache sites did not denote an error in cache retrieval. These results suggest that kangaroo rats can remember the locations of food caches, and can relocate cache sites even when there is no odour of buried seeds. To estimate the advantage enjoyed by the forager with greater information, a second experiment compared an owner's success in retrieving its caches with the success of naive kangaroo rats searching for these same caches. Nine wild-caught kangaroo rats were allowed to search for caches that were distributed in the same spatial pattern as that created by one kangaroo rat from the first experiment. The naive subjects found significantly fewer caches than had the cache owner in the same length of time. This suggests that the use of spatial memory by a Merriam's kangaroo rat to relocate its food caches gives it a competitive advantage over other kangaroo rats that may be searching for its caches.